Based on the previous studies and development practice in recent 10 years, a quantitative evaluation method for the adaptability of well patterns to ultra-low permeability reservoirs was established using cluster anal...Based on the previous studies and development practice in recent 10 years, a quantitative evaluation method for the adaptability of well patterns to ultra-low permeability reservoirs was established using cluster analysis and gray correlation method, and it includes 10 evaluation parameters in the four aspects of optimal evaluation parameters, determination of weights for evaluation parameters, development stage division, and determination of classification coefficients. This evaluation method was used to evaluate the well pattern adaptability of 13 main ultra-low permeability reservoirs in Triassic Chang 6 and Chang 8 of Ordos Basin. Three basic understandings were obtained: Firstly, the well pattern for ultra-low permeability type-I reservoirs has generally good adaptability, with proper well pattern forms and well pattern parameters. Secondly, square inverted nine-spot well pattern is suitable for reservoirs with no fractures; rhombic inverted nine-spot injection pattern is suitable for reservoirs with some fractures; and rectangular well pattern is suitable for reservoirs with rich fractures. Thirdly, for the ultra-low permeability type-Ⅱ and type-Ⅲ reservoirs, with the principles of well pattern form determination, the row spacing needs to be optimized further to improve the level of development of such reservoirs.展开更多
For thin oil rim reservoir with gas cap and edge water, it is helpful to improve the development effect to find out the distribution law of remaining oil in this kind of reservoirs. For this reason, taking the narrow ...For thin oil rim reservoir with gas cap and edge water, it is helpful to improve the development effect to find out the distribution law of remaining oil in this kind of reservoirs. For this reason, taking the narrow oil rim reservoir with gas cap and edge water of Oilfield A in Bohai Sea as a case, the main controlling factors, including reservoir structure, fault, gas cap energy, edge water energy and well pattern, affecting the distribution of residual oil in this kind of reservoir were analyzed by using the data of core, logging, paleogeomorphology and production. Then, the distribution law of remaining oil was summarized. Generally, the remaining oil distribution is mainly potato-shaped or strip-shaped in plane. Vertically, it depends on the energy of gas cap and edge water. For the reservoir with big gas gap and weak edge water, the remaining oil mainly lies in the bottom of oil column. And for the reservoir with small gas gap and strong edge water, the remaining oil mainly locates at the top of oil column. Aiming at different distribution modes of remaining oil, the corresponding potential tapping strategies of horizontal wells are put forward: in the late stage of development, for the reservoir with big gas gap and weak edge water, the remaining oil concentrates at the bottom of the oil column, and the position of horizontal well should be placed at the lower 1/3 to the lower 1/5 of the oil column;for the reservoir with small gas cap and strong edge water, the remaining oil locates at the top of the oil column, and the position of horizontal well should be put at the upper 1/5 to the upper 1/3 of the oil column height, vertically. Based on the study on remaining oil of Oilfield A, a potential tapping strategy of well pattern thickening and vertical position optimization of horizontal well was proposed. This strategy guided the efficient implementation of the comprehensive adjustment plan of the oilfield. Moreover, 18 infill development wells were implemented in Oilfield A, and the average production of the infill wells is 2.1 times that of the surrounding old wells. It is estimated that the ultimate recovery factor of the oilfield will reach 33.9%, which is 2.3% higher than that before infilling wells. This study can be used for reference in the development of similar reservoirs.展开更多
Visual models of fractured-vuggy reservoirs were designed and manufactured to conduct experiments of nitrogen assisted gravity drainage(NAGD). The impacts of flooding pattern, gas injection rate, well type, and displa...Visual models of fractured-vuggy reservoirs were designed and manufactured to conduct experiments of nitrogen assisted gravity drainage(NAGD). The impacts of flooding pattern, gas injection rate, well type, and displacement direction(vertical or horizontal) on development performances and remaining oil distribution were studied. The results show that during NAGD, the sweep scope is decided by the connections between producer and reservoir, and the local sweep efficiency is decided by fracture-vuggy configuration. The homogenous fractured reservoir has higher oil recovery, and the bigger the aperture of fracture is, the higher the recovery. The main regions of remaining oil due to poor connectivity and gas-oil gravity difference include blind fractures and vugs below the connected fractures, the bottom of vugs, and the narrow and low-angle fractures. The accumulation of remaining oil in the bottom of reservoir is easily formed and controlled by the connections between producers and reservoir. The higher the gas injection rate and the stronger the fracture heterogeneity, the earlier the gas channeling and the lower the oil recovery of the producer will be.Horizontal wells have the best development effect, so horizontal well can be applied in fractured-vuggy reservoirs without bottom water.Producers should be preferentially drilled at low structural position. Gas channeling firstly occurs in the producer at high structural position, and it should be shut in timely to improve the utilization of injected gas.展开更多
基金Supported by the China National Science and Technology Major Project(2016ZX05050 2017ZX05013-004)
文摘Based on the previous studies and development practice in recent 10 years, a quantitative evaluation method for the adaptability of well patterns to ultra-low permeability reservoirs was established using cluster analysis and gray correlation method, and it includes 10 evaluation parameters in the four aspects of optimal evaluation parameters, determination of weights for evaluation parameters, development stage division, and determination of classification coefficients. This evaluation method was used to evaluate the well pattern adaptability of 13 main ultra-low permeability reservoirs in Triassic Chang 6 and Chang 8 of Ordos Basin. Three basic understandings were obtained: Firstly, the well pattern for ultra-low permeability type-I reservoirs has generally good adaptability, with proper well pattern forms and well pattern parameters. Secondly, square inverted nine-spot well pattern is suitable for reservoirs with no fractures; rhombic inverted nine-spot injection pattern is suitable for reservoirs with some fractures; and rectangular well pattern is suitable for reservoirs with rich fractures. Thirdly, for the ultra-low permeability type-Ⅱ and type-Ⅲ reservoirs, with the principles of well pattern form determination, the row spacing needs to be optimized further to improve the level of development of such reservoirs.
文摘For thin oil rim reservoir with gas cap and edge water, it is helpful to improve the development effect to find out the distribution law of remaining oil in this kind of reservoirs. For this reason, taking the narrow oil rim reservoir with gas cap and edge water of Oilfield A in Bohai Sea as a case, the main controlling factors, including reservoir structure, fault, gas cap energy, edge water energy and well pattern, affecting the distribution of residual oil in this kind of reservoir were analyzed by using the data of core, logging, paleogeomorphology and production. Then, the distribution law of remaining oil was summarized. Generally, the remaining oil distribution is mainly potato-shaped or strip-shaped in plane. Vertically, it depends on the energy of gas cap and edge water. For the reservoir with big gas gap and weak edge water, the remaining oil mainly lies in the bottom of oil column. And for the reservoir with small gas gap and strong edge water, the remaining oil mainly locates at the top of oil column. Aiming at different distribution modes of remaining oil, the corresponding potential tapping strategies of horizontal wells are put forward: in the late stage of development, for the reservoir with big gas gap and weak edge water, the remaining oil concentrates at the bottom of the oil column, and the position of horizontal well should be placed at the lower 1/3 to the lower 1/5 of the oil column;for the reservoir with small gas cap and strong edge water, the remaining oil locates at the top of the oil column, and the position of horizontal well should be put at the upper 1/5 to the upper 1/3 of the oil column height, vertically. Based on the study on remaining oil of Oilfield A, a potential tapping strategy of well pattern thickening and vertical position optimization of horizontal well was proposed. This strategy guided the efficient implementation of the comprehensive adjustment plan of the oilfield. Moreover, 18 infill development wells were implemented in Oilfield A, and the average production of the infill wells is 2.1 times that of the surrounding old wells. It is estimated that the ultimate recovery factor of the oilfield will reach 33.9%, which is 2.3% higher than that before infilling wells. This study can be used for reference in the development of similar reservoirs.
基金Supported by the China National Science and Technology Major Project(2016ZX05014-003-004)
文摘Visual models of fractured-vuggy reservoirs were designed and manufactured to conduct experiments of nitrogen assisted gravity drainage(NAGD). The impacts of flooding pattern, gas injection rate, well type, and displacement direction(vertical or horizontal) on development performances and remaining oil distribution were studied. The results show that during NAGD, the sweep scope is decided by the connections between producer and reservoir, and the local sweep efficiency is decided by fracture-vuggy configuration. The homogenous fractured reservoir has higher oil recovery, and the bigger the aperture of fracture is, the higher the recovery. The main regions of remaining oil due to poor connectivity and gas-oil gravity difference include blind fractures and vugs below the connected fractures, the bottom of vugs, and the narrow and low-angle fractures. The accumulation of remaining oil in the bottom of reservoir is easily formed and controlled by the connections between producers and reservoir. The higher the gas injection rate and the stronger the fracture heterogeneity, the earlier the gas channeling and the lower the oil recovery of the producer will be.Horizontal wells have the best development effect, so horizontal well can be applied in fractured-vuggy reservoirs without bottom water.Producers should be preferentially drilled at low structural position. Gas channeling firstly occurs in the producer at high structural position, and it should be shut in timely to improve the utilization of injected gas.
